Sealed beam headlights that have been deployed with tactical vehicles for many years have poor performance characteristics compared with today's automotive lighting systems. A common headlamp in tactical vehicles is an incandescent, sealed beam headlamp containing two filaments, one for high beam and one for low. These headlamps produce on average up to 75,000 cd (candela), and 100 m visibility at 2 lx (lux). The color temperature for incandescent headlamps is about 3000 K, giving the light a warm yellowish appearance.
Halogen headlamps are a significant improvement over incandescent bulbs, producing more lumens per watt. This means that more light can be produced with the same amount of power. Most halogen lights can reach a luminous intensity of approximately 150,000 cd. Halogen headlamps operate at much higher temperatures than incandescent bulbs, increasing the chance of headlamp lens breakage and heat damage to the lamp housing.
HID (high intensity discharge) headlamps (using typically a xenon gas) are the latest technology in automotive lighting systems. Like halogen headlamps, HID headlamps consume less power than incandescent headlamps and have a luminous intensity even greater than halogens, approximately 200,000 cd. The color temperature of an HID light is in the range of 5000 K, similar to daylight. The average lifespan of an HID bulb is 2000 hours, roughly 5 times longer than a standard incandescent headlamp. HID headlamps work by producing an electric arc through a gas (typically xenon for automotive applications). A small lighting ballast is required to produce the arc when used with automotive voltages. (A lighting ballast is a piece of equipment required to control the starting and operating voltages of electrical gas discharge lights, such as HID lamps, and also fluorescent and neon lights. The term lighting ballast for a light can refer to any component of a circuit intended to limit the flow of current through the light, from a single resistor to more complex devices.)
Military “blackout” operations present even greater challenges: operating a vehicle at night, at moderately high speed, without being detected by enemy forces. Traditional blackout lights that have been deployed on tactical vehicles provide a very small amount of visible light illumination directly in front of the vehicle bumper. Many operators consider this to be ineffective especially when driving at higher speeds.
Night vision goggles (NVGs) along with infrared lighting have significantly improved low-light and blackout operations. NVGs used without providing any sort of illumination are, however, generally considered inadequate for such operations.
It is generally considered to be highly advantageous to provide infrared (IR) illumination in a field of view, instead of relying on infrared produced by objects in the field of view.
IR illumination of a field of view is a great help in blackout operations, dramatically increasing the effectiveness of even lower-performing NVGs. IR illumination is often produced from an incandescent lamp using a blackout filter/lens that passes only IR radiation from the incandescent lamp. Producing IR illumination in this way, though, is inefficient, since the lamp still produces visible light too, and only a small portion of the radiation produced by the lamp is passed as IR. In addition, it is difficult to block all visible light, and further, the filter/lens must be mechanically moved into place, which results in what is often an unacceptable conversion time to switch between visible and infrared illumination mode.
What is needed then is a lamp that provides both visible light and also IR illumination, both of sufficient intensity for vehicle operation (at night) at reasonable speeds, but without generating so much heat that heat dissipation is problematic, and also that switches from visible light to IR in an acceptable time.